1. Field of the Invention
The present invention concerns a sliding sleeve valve for production, injection and cementing in wells in geological strata.
2. Related and Prior Art
Production of oil and gas, geothermal applications and drilling of wells for water involves drilling through rock, soil, or other geological formations. Oil/condensate, gas, water, geothermally heated water etc. is hereinafter referred to as production fluid, and can, e.g. in production of hydrocarbons and in geothermal applications, comprise several phases. The formations containing production fluids are usually divided into layers or strata. The drilling may occur vertically through one or more strata in order to reach the desired layer, and then possibly horizontally along one or more strata to provide as efficient wells as possible.
Drilling in geological strata is done by rotating a drill bit at the end of a drill string and force it in the desired direction through geological layers or strata to form a wellbore. Once a predetermined length of wellbore is drilled, the drill string with the drill bit may be pulled out, and the wellbore may be lined with a steel pipe called a casing or liner. Hence, an outer annular space is formed between the casing and the formation. It is common practice to cement the casing to the formation by filling all or part of the outer annular space with cementing slurry. A fully or partially cemented casing stabilizes the formation, and at the same time makes it possible to isolate certain layers or regions behind the casing for retrieval of hydrocarbons, water or geothermal heat. It is well known to anyone skilled in the art that e.g. epoxy-resin-based cementing slurries in some cases are better suited for the task than cement based mixtures. The terms “cement” and “cementing” are thus to be construed generally as injection of a viscous slurry which then hardens, for the purpose of retaining the casing in the formation, and/or stabilize the formation, and/or create a barrier between different zones, and not exclusively as use of cement.
Cementing tools or valves may be included in the casing at predetermined locations. When a segment of casing is to be cemented, the cementing valve is opened and cement slurry is pumped down the casing, out through the valve-ports, and into the outer annular space. Those skilled in the art will be familiar with the use of suitable plugs, staged cementing in which a first batch of cement is allowed to set before the next batch of liquid slurry is pumped into the annular space above it, thus reducing the hydrostatic pressure from the cement which might otherwise harm or damage a weak formation and other cementing techniques and details.
When a well is drilled and lined with a casing, a return flow path from the formation around the casing to the surface must be established. In some instances it is possible to penetrate the casing by setting off explosive charges at one or more predetermined depths to enable radial flow of production fluid from the formation into the casing. In other instances, the casing may be provided with prefabricated holes or slits, possibly combined with sand screens. In many applications, the combination of high hydraulic pressure and relatively porous production strata implies a substantial risk for damage on the formation if explosives are used to penetrate the casing. In these cases, common practice is to use valve sections with radially extending openings which are opened to allow radial flow of cement or epoxy/resin out of the casing for stabilizing and retaining the casing in the formation, for radial flow of injection fluid from inside the pipe to the surrounding formation to maintain or increase the hydraulic pressure in the formation, and/or for radial flow of production fluid from the formation into the casing. Such valve sections designed for inclusion in a tubular, usually by means of threaded couplings of the same kind as used when connecting the pipe segments to a string, are called “valves” in the following for simplicity.
It is also common practice to insert a production pipe into the casing. The inner annular space between the casing and the production pipe is filled with a suitable liquid or mud, and is generally used to maintain and increase hydraulic pressure. The production pipe is in these cases used as return path, and conveys the production fluid to the surface. When using a production pipe within the casing, it is of course also necessary to provide the production pipe with openings or apertures for production fluid, and it may be necessary to isolate production zones from the liquid or mud in the inner annular space between production pipe and casing. Isolating different zones can be accomplished by using mechanical plugs called “packers” rather than by using cementing slurry. Such packers are mainly used in the inner annular space between production pipe and casing, because it may be problematic to achieve sufficient sealing against the formation, especially if the formation is porous. Valves corresponding to the valves described above can be included in the production pipe, and they can be opened once they are localized in a production zone.
During cementing, injection and production in wells as those described above, the possibility for large differential pressures between different zones increase with increasing depth. Production of hydrocarbons from strata deep below a seabed and geothermal applications are both likely to involve large pressures. Isolation of zones and injection of liquid or gas to increase the pressure in the production regions can lead to correspondingly large differential pressures.
Hydraulic fracturing, poses particularly demanding requirements to the design, robustness and durability of the valve. In hydraulic fracturing, a mixture containing e.g. 4% small ceramic particles is injected into the formation at a pressure well above the formation pressure. Fractures in the formation are expanded by the pressure and filled with these particles. When the hydraulic pressure is removed, the particles remain in the fractures and keep them open. The purpose is to improve the inflow of production fluid from the formation.
U.S. Pat. No. 3,768,562 discloses a cementing tool comprising an inner valve sleeve slidably mounted within an outer cylindrical housing. The housing has one or more cementing ports through the wall in the area where the valve sleeve is slidably located. The valve sleeve has matching cementing ports through the wall arranged so that the ports in the valve sleeve will align with the ports in the housing when the sleeve is in its uppermost position within the housing. The valve sleeve and housing have appropriate inner and outer diameters so that the sleeve fits just loosely enough within the housing to allow it to slide in the housing. An inner annular recess runs circumferentially around the interior wall of the housing, intersecting the ports therein. A corresponding outer annular channel runs circumferentially around the exterior wall of the sleeve, in the area of and intersecting the ports therein. If the sliding sleeve is rotated within the housing, the annular recess and channel allow fluid communication through the ports should the ports in the housing and sleeve, respectively, not be exactly in line when the sleeve is moved to its open position.
The sliding sleeve valve of U.S. Pat. No. 3,768,562 can also be included in a production string or any other tubular. As the tubulars (casings, drill strings, production pipes etc) usually are assembled from lengths of pipe that are threaded together, the common way to include such valves or tools is to provide them with a suitable threads at each end, and to include them in the tubular just like the other segments of pipe.
U.S. Pat. No. 4,669,541 discloses a stage collar for cementing a well casing in stages, which can be opened and closed by axial movement of the drill pipe and which provides a direct passage from the drill pipe to the casing annulus without entering the casing interior. A stage collar is shown, which can be opened and closed by axial movement of the drill pipe and, when closed after a cementing operation, is locked closed so as not to be accidentally reopened. The stage collar comprises a ported sleeve adapted to slide between an open position and a closed position, which closing sleeve have ports which are alignable with corresponding ports in the housing. Anti-rotation lugs are received in an axial sleeve recess in the sleeve's outer surface, preventing the closing sleeve from rotating in the ported housing. The stage collar further comprises a separate shift sleeve used to operate or actuate the closing sleeve. An expandable latch ring locks the closing sleeve in the closed position when cementing is complete, and additionally ensures that the shift sleeve, shifting tool and drillpipe cannot be retrieved with axial pipe movement until the stage collar is locked closed.
One problem with known valves of the types discussed above, is that they are not well adapted to applications with gas, vapour and liquid at very high pressures. This limits the use of such valves in environments where gas or vapour under high pressure poses strict requirements to the sealing.
Another problem with prior art valves of the kind discussed above, is that seals can be blown or torn out by the fluid flow when they are opened and there is a large differential pressure over the valve. A valve which is damaged in this manner can no longer be closed. In addition, the pressure shock that arises from such an event may also damage equipment further downstream in the well, i.e. closer to the surface. In order to prevent valves being damaged in this manner, i.e. that the seals are blown or torn out, the pressure difference between different zones in the well must be kept within margins determined by the valves.
U.S. Pat. No. 6,763,892 discloses a sliding sleeve valve, wherein the closing sleeve comprises primary, secondary and tertiary seals acting in cooperative combinations. The valve has a plurality of pressure equalization ports in the sliding sleeve that are intended to communicate with the main body ports prior to the sliding sleeve ports when opening and subsequent to the sliding sleeve ports when closing. This is intended to permit equalization of fluid pressure across the valve before it is fully open or fully closed in order to reduce wear on the seals.
Another problem with known valves is that debris, i.e. larger or smaller particles contaminating the well fluid, is deposited on faces in the valve. Corrosion and scaling may also cause small create small irregularities, possibly causing inferior sealing and reduced operational reliability.
A further problem with prior art valves is that they comprise many parts, making them relatively expensive to manufacture. Valves for high pressure applications may also comprise several high-pressure seals, which are more expensive than seals with lower pressure ratings. Also, some applications, e.g. hydraulic fracturing, require hard surfaces in the ports. Insets of e.g. tungsten carbide may be used, adding to the cost due to the material, and also because hard materials are more expensive to machine when manufacturing the valve.
A further problem with prior art valves is that they lack means to indicate directly if they are in open or closed position.